When you’re deciding on your computer backup strategy, make sure it includes a form of “versioned backup.”
A Memory For Your Files
Before personal computers, we did our work on paper. The paper approach has a built-in “memory.” If you rewrite a paper document, the old document sticks around until you take action and throw it away. By default you have versioned backup. Even after you throw it away you could still get it back if you’re willing to dumpster-dive and you do it before the garbage truck arrives.
When we switched to personal computers for documents, we lost that “memory.” When you save a new version of your document on your computer, the old version is immediately obliterated — gone forever! It’s unfortunate because having the old versions can be a huge time saver. When you’ve made a mess of things and you want to start over, when you realize you deleted a file that you still need, or when a file becomes unreadable for whatever reason, going “back in time” to get an old version saves the day.
The “trash can” in Windows and OS X isn’t a complete solution, because it only holds onto files you’ve deleted. If you open a document, make some changes, and then click “Save”, the previous version of the document doesn’t go into the trash can.
Apple has tried to provide a form of versioned backup through OS X Lion’s Auto Save and Versions feature. But it only works in apps that have added support for that feature, so it’s not a complete solution.
So, make sure you include a product in your backup strategy that keeps versions. Time Machine (Apple’s built-in backup app) does it for local backups. Arq does it for online backups. Dropbox does it to some extent (it keeps a few revisions of each file).
Cloning tools like SuperDuper don’t do it (but they have other advantages like quick recovery time).